1. Field of the Invention
The invention relates to an apparatus and a method of producing a focused ion beam (FIB) and a focused electron beam (FEB), and more particularly to an apparatus and a method of extracting both ion and electron beams from a liquid metal ion source (LIMS).
2. Description of the Related Art
The technique of FIB has been applied broadly in inspecting and mending integrated circuits (ICs) to achieve the objects of improving yield and enhancing throughput. Recently, a FIB produced by an LMIS has not only been applied in scanning ion microscopy (SIM), high spatial resolution secondary ion mass spectrometry (SIMS), but also in semiconductor fabrication process, for example, selective area molecular beam epitaxy, beam-induced selective area material deposition or etching, photolithographic mask repair, and sample preparation for transmission electron microscopy (TEM).
Inspection of a microstructure is conducted by a FIB-based microlithography and a microanalytic process. In principle, such inspection can be achieved by operating FIB as a SIM, which is similar to scanning electron microscopy (SEM). The main difference between SIM and SEM is that a SEM scans a FEB across the sample surface to achieve microscopic imaging, while a SIM scans a FIB. Due to the very large momentum of ion beam, a FIB is highly destructive. Material scanned by FIB is continuously sputter-removed from a sample surface during a SIM observation. Thus, details of a microstructure could have been eroded away quickly before a meaningful measurement is made. The less destructive SEM is therefore preferred in the application of inspection, and the SIM is preferred in the application of microsurgical operation.
A conventional dual beam system comprising two independent optical columns is shown as FIG. 1. In the figure, a FEB 10' is produced by an optical column 10, and a FIB 12' is produced by the optical column 12. Both the FEB 10' and the FIB12' are pointed exactly on the same spot of the sample 14, so that an identical area of the sample 14 is observed by both FEB 10' and FIB 12'. A detector 16 is positioned aside of the optical column 12 for detecting signal.
The cost of the above dual beam system is twice of a single column system. The disadvantage in application is that to have the FEB 10' and the FIB 12' incident on a same spot of the sample 14, the sample 14 has to be rotated with an angle of .theta. for FEB 10' operation. A displacement is inevitably caused during rotation. Therefore, loss of precise registration is resulted. During the subsequent process such as high precision optical cutting or material deposition, the accuracy is decreased.
If the loss of precise registration is overcome, the images obtained by FEB and the FIB are still different. It is because that only one detector is in use. The sample has been rotated, so that the prospectives of the images are different. While positioning FIB, systematic mistakes happen.
Thus, the development of a single optical column with both FIB and FEB are necessary. In U.S. Pat. No. 4,740,698, a focused ion/electron beam (FIEB) system is disclosed. An LIMS and a separate field emission electron source (FEES) mounted on a changeover gadget are employed to switch between FIB and FEB. The drawback of the two-tip system is in the displacement of source position. Such displacement leads to a relative shift between the FIB and the FEB images. The operation of FIB is complicated. In addition, once the tip of the FEB is damaged, it can not be repaired.